More than 500 islands and islets make up the Inner and Outer Hebrides. Often cloaked in mist and rain and nearly always wind-scoured, they're surrounded by waters temperamental enough to test the most skilled captain, seas that can vary in a day from a silken ripple of improbably tropical blue to a roiling assault of gunmetal and spume. For thousands of years humans have struggled to survive here. Even so, Celts and Vikings, then Scots and English, fought to rule these shores. Today only a few dozen of the Hebrides are inhabited. "The islands are a challenge," Robson says. "Some visitors call them bleak, but that just means they're not really paying attention."

Between battles the isles got precious little attention. The famously cranky 18th-century London intellectual Samuel Johnson declared that mainlanders to the south knew no more of them than they did "of Borneo or Sumatra." What little was written focused on "improving" the islands: What crops could be grown? What resources exploited? How large a population could the various islands support, and what sort of rents could they generate for their landlords? Johnson mostly filled the journal of his Hebridean journey with complaints about the difficulties of travel and the rustic accommodations that he endured.

But even as Johnson grumbled, a different set of ideas about the value of rugged places was gaining importance. Scottish Enlightenment thinkers, particularly philosopher David Hume and geologist James Hutton, unshackled intellect from piety, insisting that the ways of the world be learned by direct experience, rather than by reference to ancient and sacred authorities. To these men nature was not merely a wilderness to be tamed; it was the Earth's own textbook.

Some of its most dramatic pages were read on the Hebrides. In 1800 geologist Robert Jameson (who later served as Charles Darwin's professor at the University of Edinburgh) published Mineralogy of the Scottish Isles in two volumes, offering detailed descriptions of hundreds of Hebridean sites. On Islay, Jameson noted shell deposits far from the highest tides: "proofs," he wrote, "of the retiring of the sea from the land." Scientists now know that these fossil beaches, elevated as much as 115 feet above the present waterline, record the passing of the last great ice age. As glaciers blanketing the island began to melt 15,000 years ago, relieving it of the huge weight of ice, the land began to rebound, eventually lifting the coastline high and dry from the sea.

On Skye, Jameson declared that "this island appears, at some former period, to have been very much exposed to violent convulsions." The spiky arc of the Black Cuillin range, rising more than 3,000 feet above sea level, is indeed the remains of a volcano. The outer structures have long since disappeared, revealing the stark and convoluted shape of the deep magma chamber that seethed here 60 million years ago.